The present invention relates to a novel fluorine-containing copolymer and a composition containing the same suitable for coating, forming or molding.
Paints containing fluorine-containing polymers as a base material give coating films excellent in chemical resistance, weatherability, stain resistance, heat resistance, and the like, and they are used in a variety of uses wherein such excellent properties are sufficiently exhibited.
However, usual fluorine-containing polymers have poor solubilities in solvents and, even if they are soluble in solvents, the kinds of solvents to be used are limited. Further, since the usable solvents have high boiling points, heat treatment at high temperature is required after coating.
To overcome those disadvantages, there has been proposed the use of fluorine-containing polymers in combination with methyl methacrylate polymers. However, vinylidene fluoride polymers are the only polymers that have been found heretofore as a fluorine-containing polymer capable of being mixed uniformly with methyl methacrylate polymers, with the exception of fluorine-containing methacrylate copolymers having a low fluorine content. Generally, solvents capable of dissolving the vinylidene fluoride polymers are limited to special solvents having a high boiling point, such as N,N-dimethylformamide and N,N-dimethylacetamide, which require high temperature for drying a coating. A commercially available paint containing a vinylidene fluoride polymer and a methyl methacrylate polymer must be baked at a high temperature to obtain a coating film.
Recently, research for development of a fluorine-containing resin paint which is curable at room temperature and does not require high temperature baking has been conducted. For instance, attempts were made to obtain a fluorine-containing copolymer having an improved solubility which is prepared by copolymerizing vinylidene fluoride and other fluorine-containing monomers such as tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene. However, since vinylidene fluoride has a poor copolymerizability, a fluorine-containing comonomer used as a functional monomer imparting room temperature curability to the resulting copolymer is limited to a special one. It is the present situation that no practical fluorine-containing copolymer curable at room temperature is obtained.
There has been also proposed a copolymer of fluoroolefin, cyclohexyl vinyl ether and other comonomer for paint curable at room temperature (see Japanese unexamined patent publication Nos. 55-25414, 57-34107 and 57-34108). However, this copolymer has a problem that it cannot be blended uniformly with a methyl methacrylate polymer having good transparency.
A solution containing a fluoroolefin copolymer having hydroxyalkyl groups, (which is prepared, for instance, by solution-polymerization of hydroxyalkyl vinyl ether with fluoroolefin, and if needed, also with alkyl vinyl ether or fluoroalkyl vinyl ether), is used as it is or after dilution with aromatic hydrocarbons or thinners for paints, as a base resin for room temperature curing paints.
Paints using the fluoroolefin copolymer as a base resin give coating films having excellent properties inherent in fluorine-containing polymers as mentioned above, but, generally, they are poor in storage stability, that is, they tend to generate acids which lower the pH value thereof to cause gelation.
On the other hand, methyl methacrylate polymers are widely used in a variety of products such as lighting apparatuses, household electric appliances, instrumental boards, parts of automobiles and containers, due to their high transparency. However, the methyl methacrylate polymers have a drawback in that the transparency thereof is liable to be lowered by staining due to their poor stain resistance.
Heretofore, as to methyl methacrylate polymers, much research has been conducted to improve the stain resistance and lower the refractive index with retaining the excellent transparency. However, the only method found heretofore use, in combination with the methyl methacrylate polymers, vinylidene fluoride polymers which have a drawback that they are soluble in only specific solvents.